1. Field of the Invention
The present invention relates in general terms to rotary electrical machines.
More precisely, the invention relates to rotary machines which incorporate permanent magnets integrated into the rotor or stator of the machine.
2. Description of Related Art
Numerous embodiments of such machines exist.
In these known forms of construction, the magnets are generally made exclusively of ferrite, or they all contain rare earths.
Each of these two types of magnets has certain specific advantages:                for equal performance, the magnets that contain rare earths are more compact, which enables the machines to be accommodated in a smaller space,        on the other hand, ferrite magnets lead to greater bulk. However, the cost of these magnets is substantially less than that of the magnets that contain rare earths, the use of which raises the selling price of the machine.        
According to the requirements and objectives as to size and cost linked to the design of a rotary machine, either ferrite magnets or magnets containing rare earths will therefore be selected for incorporation in the machine.
In the document JP-A-57 097 357 a rotary machine was disclosed which combined the advantages quoted above in connection with the two respective types of magnets currently used in rotary machines.
In that document, N (north) and S (south) magnets are disposed alternately around the axis of rotation of the rotor of the electrical machine. These N and S magnets are surface mounted, and produce a flux which is essentially radial as in FIGS. 1a, 1b, 1c, 1d. 
It can be desirable to optimise this combination even more, in particular so as to obtain a further reduction in costs.